A well-trained nonsalient shape captures attention with delayed inhibition of return.

Numerous studies adopting Posner peripheral cueing paradigms have shown that exogenous attentional orientation (EAO) to a salient-but-irrelevant stimulus involves two opposing attentional processes: early attentional capture and late attentional suppression. Recent evidence has indicated that long-term perceptual learning can induce involuntary attentional capture by nonsalient shapes. However, it remains unclear whether a well-trained nonsalient shape could exhibit a biphasic pattern of EAO similar to that observed with physically salient stimuli, including both an early exogenous attentional shift and a late inhibition of return (IOR). Through both a perceptual learning task and a classic peripheral cueing task, the current study showed that a well-trained nonsalient shape cue could exhibit a biphasic pattern of EAO. When compared with an untrained shape, a well-trained nonsalient shape facilitated subsequent target detection at short cue-target onset asynchronies (CTOAs, 200-300 ms) and deteriorated target detection at a relatively long CTOA (800 ms), but not at 400- to 600-ms CTOAs. As a comparison, a detectability-matched onset cue or luminance contrast cue elicited a facilitatory effect at 200- to 300-ms CTOAs and an inhibitory effect starting from 400-ms CTOA. A control eye-tracking experiment suggested that the absence of IOR effects at 400- to 600-ms CTOAs in the trained cue task was not due to fewer eye movements during the task. Our results indicated that, as opposed to physically salient stimuli, a well-trained nonsalient shape induced delayed IOR after an evident exogenous shift of visual attention. The different patterns of EAO processes support the notion that prior experience (such as perceptual learning) plays a unique role in modulating our exogenous attention. Possible underlying mechanisms are proposed.